How do I know if my water pump needs replacement?

If the mechanic saw it leaking then he would have had to add coolant. have you been checking your coolant reservoir for coolant level? If you wait for it overheats then that is to late. You should check all your fluid levels once a week.

It's common if you don't perform the preventive maintenance required. You have a leak. Coolant doesn't evaporate. If you had to add a half gallon of coolant you have a leak. Sometimes water pumps leak only hot or running. If there was a presence of coolant at the weep hole on the water pump then you need a water pump. The water pump is timing belt driven. It's about 5 to 6 hours to replace. What else do they want to replace with the water pump. It's 6 years old. If it was my truck I would replace the timing belt to. Just because of age not mileage. A timing belt is rubber. Rubber has a age life in addition to a mileage life. I agree with PARTS GUY. You need to check all your fluids at least once a week. Takes about ten minutes.

a small leak now may be a large leak very soon. I would be pro active and get it replaced before it lets you down. Roy